Method for transmitting control information in wireless communication systems

ABSTRACT

When a plurality of terminals share the same resources in a wireless communication system, and when control information such as acknowledgement/negative acknowledgement (ACK/NAK) information or scheduling information is transmitted, a method of efficiently performing code division multiplexing (CDM) is required to distinguish the plurality of terminals. In particular, it is necessary to develop a method by which a code sequence of CDM can be selected and used according to each cell condition. Provided is a method of forming a signal in a wireless communication system in which a plurality of terminals commonly share frequency and time resources. The method includes the operations of receiving condition information in a cell; selecting one of a plurality of time domain orthogonal sequences having different lengths, according to the condition information; and allocating the selected time domain orthogonal sequence to a control signal symbol block.

CROSS REFERENCE TO RELATED APPLICATION(S)

This application is a continuation of U.S. application Ser. No.15/452,541, filed on Mar. 7, 2017 (now pending), which is a continuationof U.S. patent application Ser. No. 13/755,497 filed on Jan. 31, 2013(now U.S. Pat. No. 9,620,233), which is a continuation of U.S. patentapplication Ser. No. 12/664,925 filed on Dec. 16, 2009 (now U.S. Pat.No. 8,391,232), which is a national stage application under 35 USC 371of International Application No. PCT/KR2008/003573 filed on Jun. 23,2008, which claims the benefit of Korean Application No. 10-2008-0058985filed on Jun. 23, 2008, Korean Application No. 10-2007-0079785 filed onAug. 8, 2007, and Korean Application No. 10-2007-0060852 filed on Jun.21, 2007 in the Korean Intellectual Property Office, the content ofwhich is incorporated herein by reference in their entirety.

TECHNICAL FIELD

The present invention relates to a method and apparatus for transmittingcontrol information in a wireless communication system, and moreparticularly, to a method and apparatus for transmitting controlinformation such as acknowledgement/negative acknowledgement (ACK/NAK)information or scheduling request information by using resources sharedby each of a plurality of terminals.

When a plurality of users (terminals) simultaneously use an ACK/NAKchannel in a wireless communication system, a code division multiplexing(CDM) technique may be used in the plurality of terminals. In CDM, eachof the plurality of terminals transmits a result obtained by multiplyinga signal to be transmitted by a spreading code allocated to each of theplurality of terminals.

The present invention relates to identifying signals of a plurality ofterminals when the plurality of terminals use a spreading code along afrequency axis and a spreading code along a time axis.

The present invention is derived from research supported by theInformation Technology (IT) Research & Development (R&D) program of theMinistry of Information and Communication (MIC) and the Institute forInformation Technology Advancement (IITA) [Project management No.:2005-S-404-13, Research title: Research & Development of RadioTransmission Technology for 3G Evolution].

BACKGROUND ART

A receiver transmits an acknowledgement (ACK) signal to a transmitterwhen the receiver succeeds in demodulating received data, and transmitsa negative acknowledgement (NAK) signal to the transmitter when thereceiver falls to demodulate the received data. Each of the ACK/NAKsignals is expressed as one bit per codeword. The ACK/NAK signals shouldbe enabled to be simultaneously transmitted by a plurality of users(terminals) using given time and frequency resources throughmultiplexing.

Such multiplexing techniques are classified into frequency divisionmultiplexing (FDM) and code division multiplexing (CDM). FDM is a formof multiplexing where a plurality of different terminals use differenttime/frequency resources, whereas CDM is a form of multiplexing where aplurality of different terminals use the same time/frequency resourcesbut transmit results obtained by multiplying signals by specificorthogonal codes so that a receiver can identify the plurality ofdifferent terminals.

In an uplink, a Zadoff-Chu sequence having an ideal peak to averagepower ratio (PAPR) is often used. Such a Zadoff-Chu sequence can achieveorthogonality between terminals through a cyclic delay, instead ofmultiplying a signal by a specific code in a frequency domain.

An uplink ACK/NAK signal is required for a terminal to inform a basestation of a successful or unsuccessful (ACK or NAK) receipt of downlinkdata, and requires one bit per codeword which is used to transmit thedownlink data.

FIG. 1 illustrates time/frequency resources used by a terminal toperform uplink ACK/NAK signaling in a 3rd generation partnershipprojection long term evolution (3GPP LTE) system. Referring to FIG. 1,resources used by one control channel are grouped into two separateresource blocks. Each of the two resource blocks includes N subcarriersalong a frequency axis, and 7 orthogonal frequency division multiplexing(OFDM) symbols, which corresponds to one slot, along a time axis. Oneslot has a time duration of 0.5 ms.

In FIG. 1, a plurality of terminals may commonly use one controlchannel. That is, a control channel A or a control channel B may beshared by the plurality of terminals.

In this case, in order to identify the plurality of terminals using thesame control channel, a specific code sequence is allocated to each ofthe plurality of terminals. That is, each of the plurality of terminalsgenerates and transmits a signal spread along a frequency axis and atime axis by using its allocated specific code.

FIG. 2 illustrates a code sequence and a symbol transmitted to each of Nsubcarriers in an ACK/NAK channel occupying a resource block thatincludes the N subcarriers along a frequency axis and 7 OFDM symbolsalong a time axis. In FIG. 2, the resource block corresponding to oneslot described with reference to FIG. 1 occupies N subcarriers on afrequency axis and includes 7 symbol blocks BL #0 through #6 on a timeaxis.

When CDM is used to identify signals of a plurality of terminals, asequence and a symbol may be mapped to each time/frequency resource asillustrated in FIG. 2. In order to identify the signals of the pluralityof terminals, a sequence is applied to each of the frequency axis andthe time axis. In FIG. 2, a reference signal is used for channelestimation, and a pre-determined signal between a terminal and a basestation is transmitted.

The base station estimates a channel by the reference signal, and uses aresult of the channel estimation so as to demodulate an ACK/NAK symboltransmitted by a control signal. Each time/frequency resource carrys outa signal multiplied by two or three symbols.

That is, a time/frequency resource on which the reference signal iscarried, is obtained by multiplying a frequency axis sequence symbolC_(q) ^(m)(k) by a time axis sequence symbol Ri (i=0, 1, 2). Atime/frequency resource on which the control signal is carried, isobtained by multiplying a frequency axis sequence symbol C_(q) ^(m)(k),a time axis sequence symbol Ci (i=0, 1, 2, 3), and an ACK/NAK symbol Q.

In FIG. 2, the frequency axis sequence symbol C_(q) ^(m)(k) indicates aZadoff-Chu sequence where N_(ZC) is the length of the Zadoff-Chusequence applied to a k_(th) subcarrier along the frequency axis, m is aprimary index, and q is a cyclic delay index, and is provided byEquation 1.

$\begin{matrix}{{{C_{q}^{m}(k)} = {\exp\lbrack {i\frac{2\pi}{N_{ZC}}{m( \frac{( {k - q} )( {k - q + 1} )}{2} )}} \rbrack}},{k = 0},1,2,\ldots\;,{N - 1}} & \lbrack {{Equation}\mspace{14mu} 1} \rbrack\end{matrix}$

One sequence is applied to each of the reference signal and the controlsignal along the time axis. That is, a sequence applied to the controlsignal in FIG. 2 is expressed as C₀, C₁, C₂, and C₃. A sequence appliedto the reference signal is expressed as R₀, R₁, and R₂.

Currently, 3GPP LTE considers a configuration in which three referencesignals per slot are used for an uplink ACK/NAK channel.

Also, in order to identify a plurality of terminals, a Zadoff-Chusequence is used along a frequency axis, and a discrete Fouriertransformation (DFT) vector, a Walsh-Hadamard sequence, or a Zadoff-Chusequence may be used along a time axis.

DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates time/frequency resources used by a terminal totransmit an uplink acknowledgement/negative acknowledgement (ACK/NAK)signal through a control channel in a 3^(rd) generation partnershipprojection long term evolution (3GPP LTE) system.

FIG. 2 illustrates a code sequence and a symbol transmitted to each of Nsubcarriers in an acknowledgement/negative acknowledgement (ACK/NAK)channel occupying a resource block that includes the N subcarriers alonga frequency axis and 7 orthogonal frequency division multiplexing (OFDM)symbols along a time axis.

FIG. 3 illustrates a slot structure of an ACK/NAK channel including 3reference signals per slot, according to an embodiment of the presentinvention.

FIG. 4 illustrates a slot structure of an ACK/NAK channel including 3reference signals per slot, according to another embodiment of thepresent invention.

FIG. 5 illustrates a slot structure of an ACK/NAK channel including 3reference signals per slot, according to another embodiment of thepresent invention.

FIG. 6 is a flowchart of a method by which a terminal selectively uses atime axis code sequence achieving orthogonality with a length of 2 or 4,and transmits control information to a base station according to anembodiment of the present invention.

FIG. 7 illustrates a base station apparatus in a wireless communicationsystem, according to an embodiment of the present invention.

FIG. 8 illustrates a terminal apparatus in a wireless communicationsystem, according to an embodiment of the present invention.

DETAILED DESCRIPTION OF THE INVENTION Technical Problem

When a plurality of terminals share the same resources in a wirelesscommunication system, and when control information such asacknowledgement/negative acknowledgement (ACK/NAK) information orscheduling information is transmitted, a method of efficientlyperforming code division multiplexing (CDM) is required to identify theplurality of terminals. In particular, it is necessary to develop amethod by which a code sequence of CDM can be selected and usedaccording to each cell condition.

Technical Solution

According to an aspect of the present invention, there is provided amethod of selecting a signal in a wireless communication system in whicha plurality of terminals commonly use frequency and time resources, themethod including the operations of determining condition information ina cell; transmitting information about a code sequence to be selected tothe plurality of terminals, according to the condition information inthe cell; and selecting one of a plurality of time domain orthogonalsequences having different lengths, according to the conditioninformation in the cell.

According to another aspect of the present invention, there is provideda method of forming a signal in a wireless communication system in whicha terminal selects a code according to condition information in a cell,the method including the operations of receiving the conditioninformation in the cell; selecting one of a plurality of time domainorthogonal sequences having different lengths, according to thecondition Information; and allocating a code of the selected time domainorthogonal sequence to the terminal.

According to another aspect of the present invention, there is provideda method of forming a signal in a wireless communication system in whicha terminal allocates an orthogonal code, the method performed by theterminal and including the operations of receiving an orthogonal coverindex from a base station, wherein the orthogonal cover index achievesorthogonality with a length of 2 between the terminal and a secondterminal sharing the same resources; multiplying control information bya time axis code symbol corresponding to the orthogonal cover indexalong a time axis; having a cyclic shift index along a frequency axis,wherein the cyclic shift index is the same as that of the secondterminal sharing the same resources, and multiplying the controlinformation by a frequency axis code symbol corresponding to the cyclicshift index; and transmitting the control information to the basestation.

According to another aspect of the present invention, there is provideda base station apparatus selecting one of a plurality of code sequenceshaving different lengths according to a condition in a cell in awireless communication system, the base station apparatus including acell condition determination unit determining the condition of the cellaccording to a speed condition of terminals in the cell; a code sequenceselection information transmitting unit transmitting code sequenceselection information, which is determined according to the determinedcondition of the cell, to the terminal; and a code sequence selectionunit selecting a code sequence which is determined according to thedetermined condition of the cell.

According to another aspect of the present invention, there is provideda terminal apparatus selecting one of a plurality of code sequenceshaving different lengths according to a condition in a cell in awireless communication system, the terminal apparatus including a codesequence selection information receiving unit receiving code sequenceselection information from a base station apparatus, wherein the codesequence selection information constitutes information about a length ofa code sequence to be selected; a code sequence selection unit selectingone of the plurality of code sequences having different lengths,according to the received code sequence selection information; and acode sequence allocation unit allocating the selected code sequence to aterminal.

Advantageous Effects

According to the present invention, when a plurality of terminalssimultaneously use an acknowledgement/negative acknowledgement (ACK/NAK)channel in a wireless communication system, code division multiplexing(CDM) is performed and a spreading code using all of a frequency axisand a time axis is used, so that the plurality of terminals can beefficiently identified.

MODE OF THE INVENTION

A code allocation method for efficiently identifying a plurality ofterminals when they simultaneously use an acknowledgement/negativeacknowledgement (ACK/NAK) channel in a wireless communication systemaccording to the present invention will now be described more fully withreference to the accompanying drawings, in which exemplary embodimentsof the invention are shown.

Detailed explanation will not be provided when it is determined thatdetailed explanations about well-known functions and configurations ofthe present invention may dilute the point of the present invention.Terms used hereinafter are used considering the functions in the presentinvention and may be changed according to a user's or operator'sintention or usual practice. Accordingly, the terms will be definedbased on the entire content of the description of the present invention.

In the present invention, control information may be an ACK/NACK(NAK)signal, scheduling request information, channel quality indication (CQI)Information, precoding matrix indicator (PMI) Information, and rankIndication (RI) information, but the present invention is not limitedthereto.

In embodiments of the present invention, an ACK/NAK signal is describedas the control information. However, it will be understood by one ofordinary skill in the art that the embodiments may be applied totransmission of other control information.

In particular, the term “frequency axis code” or “frequency axis codeindex” used hereinafter is interchangeable with “cyclic shift” or“cyclic shift index,” and the term “time axis code” or “time axis codeindex” used hereinafter is interchangeable with “orthogonal cover” or“orthogonal cover index”.

Also, the term “frequency axis code sequence” used hereinafter has thesame meaning as “frequency domain identification sequence” or “frequencydomain orthogonal sequence”, and the term “time axis code sequence” usedhereinafter has the same meaning as “time domain identificationsequence” or “time domain orthogonal sequence”.

FIGS. 3 through 5 illustrate slot structures of an ACK/NAK channel,according to embodiments of the present invention. Referring to FIGS. 3through 5, one slot includes 3 reference signals and 4 control signals,but the number of reference signals and control signals per slot may bedifferent.

In order to identify signals of a plurality of terminals, a receivershould be able to receive and identify reference signals transmitted bythe plurality of terminals, and also should be able to receive andidentify control signals transmitted by the plurality of terminals. Asdescribed above, a code division multiplexing (CDM) technique using bothfrequency and time axis resources may be used to identify the signals.

A time axis sequence used for time axis CDM is an orthogonal sequence.When the number of continuous orthogonal frequency division multiplexing(OFDM) symbols along a time axis is N_(t), a sequence length may beN_(t), and N_(t) sequences achieving orthogonality therebetween may beformed. When an i_(th) sequence is expressed as a row vectorG_(i)=[C_(i,0), C_(i,1), . . . , C_(i,N) _(t) ⁻¹], the orthogonality isexpressed by Equation 2.

$\begin{matrix}{{G_{i} \cdot G_{j}^{+}} = {{\lbrack {C_{i,0},C_{i,1},\ldots\;,C_{i,{N_{t} - 1}}} \rbrack \cdot \begin{bmatrix}C_{j,0}^{*} \\C_{j,1}^{*} \\ \cdot \\ \cdot \\C_{j,{N_{t} - 1}}^{*}\end{bmatrix}} = {{\sum\limits_{k = 0}^{N_{t} - 1}\;{C_{i,k}C_{j,k}^{*}}} = {N_{t}\delta_{i,j}}}}} & \lbrack {{Equation}\mspace{14mu} 2} \rbrack\end{matrix}$where

$\delta_{i,j} = \{ {\begin{matrix}{{1\mspace{14mu}{if}\mspace{14mu} i} = j} \\{{0\mspace{14mu}{if}\mspace{14mu} i} \neq j}\end{matrix}.} $

Theoretically, if the total number of frequency axis resources is M andone slot includes 3 reference signals in FIGS. 3 through 5, a total ofM×3 reference signals may be identified by CDM.

Also, if the total number of frequency axis resources is M and one slotincludes 4 control signals in FIGS. 3 through 5, a total of M×4 controlsignals may be identified by CDM.

However, since each terminal should transmit at least one referencesignal in order for a base station to demodulate a control signal byusing the reference signal, the total number of distinguishableterminals is M×3. In this case, an orthogonal sequence with a spreadingfactor (SF) of 3 is used for the reference signals, and an orthogonalsequence with an SF of 4 is used for the control signals.

Table 1 shows a Walsh-Hadamard code with a length of 4.

TABLE 1 Walsh-Hadamard code C₀ C₁ C₂ C₃ WC0 1 1 1 1 WC1 1 −1 1 −1 WC2 11 −1 −1 WC3 −1 −1 1 1

Since the length of the Walsh-Hadamard code is 4, the Walsh-Hadamardcode may be used in the time axis CDM for the control signals. When thetotal number of distinguishable terminals is M×3, 3 of 4 sequences maybe selected and used. For example, WC0, WC1, and WC2 in Table 1 may beused and WC3 is not used. However, it may be possible not to use one ofWC0, WC1, and WC2 but to use the remaining 3 sequences.

The method with reference to Table 1 uses an orthogonal sequence with alength of 3 for all reference signals, and uses an orthogonal sequencewith a length of 4 for all control signals, and thus 3 terminals whichuse the same Zadoff-Chu sequence along a frequency axis can beidentified. However, when a terminal has high speed, orthogonality of asequence used for the reference signals and the control signals is notachieved.

In particular, since the 4 control signals are located far away fromeach other along the time axis, the 4 control signals are morespeed-sensitive. That is, orthogonality is not guaranteed for high-speedterminals. When orthogonality is not achieved, a receiver may notidentify signals of the plurality of terminals such that CDM performancesubstantially deteriorates.

In order to solve such problems, in the case where a cell includes manyhigh-speed terminals, a length of a code sequence used in the time axisCDM for the control signals may be reduced to 2. When the length isreduced to 2, performance at high speed improves, compared to the casewhen the length is 4. However, the total number of identifiableterminals is reduced from M×3 to M×2. Although the total number ofidentifiable terminals is reduced, the orthogonality is guaranteed sothat CDM performance may be improved.

Table 2 shows a case in which a Walsh-Hadamard sequence code with alength of 2 is applied to control signals.

TABLE 2 Walsh-Hadamard code C₀ C₁ C₂ C₃ WC0 1 1 1 1 WC1 1 −1 1 −1

When the Walsh-Hadamard sequence code with the length of 2 is used inthe time axis CDM for the control signals, the total number ofdistinguishable terminals is M×2. Codes of Table 2 correspond to asubset of codes in Table 1 so that the codes of Table 2 can beimplemented without increasing additional complexity.

According to another embodiment of the present invention, two terminalssharing the same resources may receive code sequence information from abase station, wherein, according to the code sequence information, thetwo terminals have the same cyclic shift along a frequency axis and areallocated an orthogonal code sequence achieving a length of 2 along atime axis. That is, the two terminals may receive information by whichthe orthogonal code sequence such as a Walsh-Hadamard code with a lengthof 2 along the time axis may be allocated to the two terminals.

To be more specific, the two terminals using the same resources areallocated the Walsh-Hadamard code with the length of 2 shown in Table 2.Each of the two terminals receives an orthogonal cover index such as WC0or WC1, and multiplies the orthogonal cover index by control informationto be transmitted, such as ACK/NAK control information. By doing so,orthogonality is achieved so as to identify the two terminals.

Orthogonality of a time axis sequence is maintained when a length of thetime axis sequence is shorter than a coherence length of a terminal. Thehigher the speed of the terminal, the shorter the coherence length.Thus, in order to maintain orthogonality among a plurality of high-speedterminals, it is ideal when the length of the time axis sequence forachieving orthogonality is short. Hence, in a cell including manyhigh-speed terminals, it is better to use a code sequence with a lengthof 2 as shown in Table 2 than to use a code sequence with a length of 4as shown in Table 1.

At this time, terminals using the same orthogonal code sequence with alength of 2 may be located far away from each other along a frequencyaxis, so as to avoid interference. Preferably, a minimum distancebetween each of the terminals may be greater than 2.

Table 3 shows sequence allocation, according to another embodiment ofthe present invention.

TABLE 3 Control information signal sequence allocation Orthogonal Cyclicshift cover index index 0 1 2 3 0 1 7 1 2 4 10 3 4 2 8 5 6 5 11 7 8 3 99 10 6 12 11

Table 3 shows a code sequence allocation for terminals #1 through #12according to the embodiment of the present invention. Referring to Table3, it is apparent that terminals #1 and #7, and terminals #2 and #8,which are allocated the same code sequence, are separated as far as 4with respect to the cyclic shift index. Although terminal #1 andterminal #7 share the same resources, results obtained by multiplying anorthogonal sequence by control information, are transmitted so that areceiver may distinguish terminal #1 from terminal #7.

FIG. 6 is a flowchart of a method by which a terminal selectively uses atime axis code sequence achieving orthogonality with a length of 2 or 4,and transmits control information to a base station, according to anembodiment of the present invention.

First, the terminal receives code sequence selection information fromthe base station (operation 610). The code sequence selectioninformation includes information of the base station which determines acondition in a cell so as to inform the terminal whether to select atime axis code sequence with a short length or to select a time axiscode sequence with a relatively long length.

For example, in a case where the cell includes a plurality of high-speedterminals, the base station may inform the terminal to use aWalsh-Hadamard sequence with a length of 2, and may simultaneouslyinform the terminal of an orthogonal cover index achieving orthogonalitywith a length of 2. The terminal receives the orthogonal cover index,and multiplies control information by a time axis code symbolcorresponding to the orthogonal cover index (operation 620). By doingso, the terminal may be distinguished from other terminals sharing thesame cyclic shift index.

After that, the terminal multiplies the control information by afrequency axis code symbol corresponding to the cyclic shift index alonga frequency axis (operation 630). Finally, the terminal transmits thecontrol information to the base station (operation 640).

According to the embodiments of the present invention, a discreteFourier transformation (DFT) code with a length of 3 is used in the timeaxis CDM for the reference signals. In the time axis CDM for the controlsignals, one of the code sequences shown in Table 1 and Table 2 is setto be selected according to a cell condition. The base station shouldinform the terminal of a code length used by the cell. For example, inorder to inform the terminal whether the code sequence of Table 1 isused or the code sequence of Table 2 is used, the base station may use 1bit from broadcasting information in the cell.

According to information having the 1 bit, the terminal may know whetherthere are M×3 ACK/NAK channels or M×2 ACK/NAK channels, and use one ofthe M×3 or M×2 ACK/NAK channels according to a predetermined rule.

In this manner, the terminal receives information about which codesequence is to be used according to the cell condition from the basestation, and based on the information, selectively uses a sequence witha length that satisfies the cell condition. That is, in the case wherethe plurality of high-speed terminals are in the cell, a short lengthcode sequence such as a code sequence with a length of 2 may be used.Conversely, in the case where the cell does not include many high-speedterminals, a long length code sequence such as a code sequence with alength of 4 may be used. By doing so, the number of distinguishableterminals may increase.

FIG. 7 illustrates a base station apparatus 700 to which the method ofFIG. 6 is applied, according to an embodiment of the present invention.

Referring to FIG. 7, the base station apparatus 700 according to thecurrent embodiment of the present embodiment includes a cell conditiondetermination unit 710, a code sequence selection informationtransmitting unit 720, and a code sequence selection unit 730. The cellcondition determination unit 710 determines which code sequence is to beused, according to a condition in a cell. As described above, in thecase where the cell includes a plurality of high-speed terminals, ashort length code sequence may be used. However, in the case where thecell does not have many high-speed terminals, it may be more efficientto use a long length code sequence.

A result of the determination by the cell condition determination unit710 is shared between the base station apparatus 700 and a terminal soas to use a mutually pre-determined code sequence. The result of thedetermination by the cell condition determination unit 710 istransmitted to the code sequence selection information transmitting unit720. The code sequence selection information transmitting unit 720 uses1 bit from broadcasting information in the cell, thereby informing theterminal of information about which code sequence is to be selected.

It may be possible to pre-determine that when the 1 bit is 0, the codesequence of Table 1 is used, and when the 1 bit is 1, the code sequenceof Table 2 is used.

The result of the determination by the cell condition determination unit710 is also transmitted to the code sequence selection unit 730 in thebase station apparatus 700. According to the result of the determinationtransmitted from the cell condition determination unit 710, the codesequence selection unit 730 selects a code sequence to be used. That is,according to the result of the determination about the condition of thecell, a time axis sequence with a length of 2 or 4 is selected; however,the present invention is not limited to these lengths and variouslengths may be selected.

FIG. 8 illustrates a terminal apparatus 800 having a code sequenceselection function, according to an embodiment of the present invention.Referring to FIG. 8, the terminal apparatus 800 according to the currentembodiment of the present invention includes a code sequence selectioninformation receiving unit 810, a code sequence selection unit 820, anda code sequence allocation unit 830. The terminal apparatus 800 receivescode sequence selection information from a base station via the codesequence selection information receiving unit 810. According to the codesequence selection information transmitted from the base station, theterminal apparatus 800 determines a length of a code sequence to beselected by using the code sequence selection unit 820. After that, whenthe code sequence to be used is determined, the terminal apparatus 800allocates a code sequence to a terminal by using the code sequenceallocation unit 830, wherein the code sequence is pre-determined withthe base station.

In this manner, the base station and the terminal can flexibly cope witha change in the cell condition. By selecting and using different lengthsof the code sequence according to speed of the terminal in the cell,efficient communication between the base station and the terminal can beachieved.

The invention can also be embodied as computer readable codes on acomputer readable recording medium. The computer readable recordingmedium is any data storage device that can store data which can bethereafter read by a computer system. Examples of the computer readablerecording medium include read-only memory (ROM), random-access memory(RAM), CD-ROMs, magnetic tapes, floppy disks, optical data storagedevices, and carrier waves (such as data transmission through theInternet).

The computer readable recording medium can also be distributed overnetwork coupled computer systems so that the computer readable code isstored and executed in a distributed fashion. Also, functional programs,codes, and code segments for accomplishing the present invention can beeasily construed by programmers skilled in the art to which the presentinvention pertains.

While this invention has been particularly shown and described withreference to exemplary embodiments thereof, it will be understood bythose of ordinary skill in the art that various changes in form anddetails may be made therein without departing from the spirit and scopeof the invention as defined by the appended claims. The exemplaryembodiments should be considered in a descriptive sense only and not forpurposes of limitation. Therefore, the scope of the invention is definednot by the detailed description of the invention but by the appendedclaims, and all differences within the scope will be construed as beingincluded in the present invention.

The invention claimed is:
 1. A communication method comprising:transmitting, at a base station, first information to a first terminal,wherein the first information indicates a cyclically shifted sequence, afirst orthogonal sequence and a first set of uplink radio resources;transmitting, at the base station, second information to a secondterminal, wherein the second information indicates the cyclicallyshifted sequence, a second orthogonal sequence and the first set ofuplink radio resources; receiving, at the base station, a first signalthrough the first set of uplink radio resources; obtaining, at the basestation, first control information from the first signal, by using thecyclically shifted sequence and the first orthogonal sequence; andobtaining, at the base station, second control information from thefirst signal, by using the cyclically shifted sequence and the secondorthogonal sequence, wherein first two elements of the first orthogonalsequence are orthogonal to first two elements of the second orthogonalsequence and last two elements of the first orthogonal sequence areorthogonal to last two elements of the second orthogonal sequence. 2.The method of claim 1, wherein: the first orthogonal sequence is one ofthree orthogonal sequences consisting of W0 (a, a, a, a), W1 (a, b, a,b) and an additional sequence W2 which is orthogonal to W0 and W1,respectively, wherein a is a first value and b is a second value.
 3. Themethod of claim 2, wherein: the first orthogonal sequence is W0 and thesecond orthogonal sequence is W2, or the first orthogonal sequence is W2and the second orthogonal sequence is W0.
 4. The method of claim 2,wherein the first value is ‘+1’ and the second value is ‘−1’.
 5. Themethod of claim 1, further comprising: receiving, at the base station, asecond signal through a second set of uplink radio resources; obtaining,at the base station, a first reference sequence from the second signal;and obtaining, at the base station, a second reference sequence from thesecond signal; wherein: the first set of uplink radio resourcescomprises a first, second, sixth and seventh symbols in a time slot, andthe second set of uplink radio resources comprises third to fifthsymbols in the time slot.
 6. The method of claim 1, wherein the firstcontrol information is acknowledgement/negative-acknowledgement(ACK/NAK) information.
 7. The method of claim 6, wherein the secondcontrol information is another ACK/NAK information.
 8. The method ofclaim 1, wherein the cyclically shifted sequence is generated based on aZadoff-Chu sequence.
 9. A wireless communication apparatus comprising: acircuitry; wherein the circuitry is configured to: cause the apparatusto transmit first information to a first terminal, wherein the firstinformation indicates a cyclically shifted sequence, a first orthogonalsequence and a first set of uplink radio resources; cause the apparatusto transmit second information to a second terminal, wherein the secondinformation indicates the cyclically shifted sequence, a secondorthogonal sequence and the first set of uplink radio resources; causethe apparatus to receive a first signal through the first set of uplinkradio resources; obtain first control information from the first signal,by using the cyclically shifted sequence and the first orthogonalsequence; and obtain second control information from the first signal,by using the cyclically shifted sequence and the second orthogonalsequence, wherein first two elements of the first orthogonal sequenceare orthogonal to first two elements of the second orthogonal sequenceand last two elements of the first orthogonal sequence are orthogonal tolast two elements of the second orthogonal sequence.
 10. The apparatusof claim 9, wherein: the first orthogonal sequence is one of threeorthogonal sequences consisting of W0 (a, a, a, a), W1 (a, b, a, b) andan additional sequence W2 which is orthogonal to W0 and W1,respectively, wherein a is a first value and b is a second value. 11.The apparatus of claim 10, wherein: the first orthogonal sequence is W0and the second orthogonal sequence is W2, or the first orthogonalsequence is W2 and the second orthogonal sequence is W0.
 12. Theapparatus of claim 9, wherein the circuitry is further configured to:cause the apparatus to receive a second signal through a second set ofuplink radio resources; obtain a first reference sequence from thesecond signal; and obtain a second reference sequence from the secondsignal; wherein: the first set of uplink radio resources comprises afirst, second, sixth and seventh symbols in a time slot, and the secondset of uplink radio resources comprises third to fifth symbols in thetime slot.
 13. The apparatus of claim 9, wherein the first controlinformation is acknowledgement/negative-acknowledgement (ACK/NAK)information.
 14. The apparatus of claim 13, wherein the second controlinformation is another ACK/NAK information.
 15. A device for a wirelesscommunication apparatus, comprising: a circuitry, wherein the circuitryis configured to: cause the apparatus to transmit first information to afirst terminal, wherein the first information indicates a cyclicallyshifted sequence, a first orthogonal sequence and a first set of uplinkradio resources; cause the apparatus to transmit second information to asecond terminal, wherein the second information indicates the cyclicallyshifted sequence, a second orthogonal sequence and the first set ofuplink radio resources; cause the apparatus to receive a first signalthrough the first set of uplink radio resources; obtain first controlinformation from the first signal, by using the cyclically shiftedsequence and the first orthogonal sequence; and obtain second controlinformation from the first signal, by using the cyclically shiftedsequence and the second orthogonal sequence, wherein first two elementsof the first orthogonal sequence are orthogonal to first two elements ofthe second orthogonal sequence and last two elements of the firstorthogonal sequence are orthogonal to last two elements of the secondorthogonal sequence.
 16. The device of claim 15, wherein: the firstorthogonal sequence is one of three orthogonal sequences consisting ofW0 (a, a, a, a), W1 (a, b, a, b) and an additional sequence W2 which isorthogonal to W0 and W1, respectively, wherein a is a first value and bis a second value.
 17. The device of claim 16, wherein: the firstorthogonal sequence is W0 and the second orthogonal sequence is W2, orthe first orthogonal sequence is W2 and the second orthogonal sequenceis W0.
 18. The device of claim 15, wherein the circuitry is furtherconfigured to: cause the apparatus to receive a second signal through asecond set of uplink radio resources; obtain a first reference sequencefrom the second signal; and obtain a second reference sequence from thesecond signal; wherein: the first set of uplink radio resourcescomprises a first, second, sixth and seventh symbols in a time slot, andthe second set of uplink radio resources comprises third to fifthsymbols in the time slot.
 19. The device of claim 15, wherein the firstcontrol information is acknowledgement/negative-acknowledgement(ACK/NAK) information.
 20. The device of claim 19, wherein the secondcontrol information is another ACK/NAK information.